Something like that is actually impossible because these filesystems are custom made, i.e. they all (can) have a different format for storing files etc. In some cases it's possible like f.e. Sensible Software games as they use a fairly simple format and tools have been coded to read the contents of suchs disks. Without coding knowledge you will have a hard time to extract data from most NDOS games.

As you've read, there are some exemptions.
It is possible, to extract even executable files from a NDOS-disk, especially
crack and trainer intros.
But, i think most time it is impossible to make a working Amiga DOS version
of a NDOS-disk.(without Coders ability).